Meanwhile, articles are subjected to radiation in an extremely wide variety of technical fields. Various types of irradiation methods and different types of radiation are used for this, depending on the requirements for the specific use. Thus, in some technical fields, it is necessary to subject articles to radiation over a large area or in three dimensions and as uniformly as possible in so doing. This is the case, for example, when materials are to be cured or changed in some other way. Meanwhile, it has also become common practice, for example in food technology, to use certain types of radiation in order to extend the shelf life of foods.
In other technical fields, though, subregions of the article to be irradiated must be irradiated with a certain predetermined dosage, typically one that is particularly high. However, the remaining parts of the article normally should either not be irradiated at all or should be irradiated as little as possible. An example of this is the structuring of microprocessors or other microstructures or nanostructures using electromagnetic radiation (sometimes extending into the X-ray range) and image-producing masks.
The dose to be applied into the respective structures can be structured not only in two dimensions, but also in all three spatial directions. A three-dimensional structuring makes it possible, for example, to directly irradiate a volume region contained inside a body to be irradiated without having to open or damage the body (in particular, its outer sheath).
Moreover, the body to be irradiated (or a volume region to be irradiated, which is contained inside the body to be irradiated) is not limited to a static body or an immobile body. Instead, the problem often arises in actual use that the body to be irradiated or parts of the body to be irradiated (e.g., a target volume region to be irradiated) is/are moving. This movement is not limited to an inherently rigid body that is moved relative to an external coordinate system. It is also possible for there to be a relative movement between different regions of the body to be irradiated. This is not necessarily limited to translational movements only. Conceivably, there can also be other types of changes such as rotational movements and changes in density.
In order to be able to irradiate such (sometimes inherently) moving bodies, so-called four-dimensional irradiation methods are used. Ultimately, these are three-dimensional irradiation methods that have a chronological variation (with time functioning as the fourth dimension). Examples of such material irradiation methods can be found in the field of materials sciences, for example in the manufacture of highly integrated components (such as microprocessors and/or memory chips) and in the manufacture of microstructured and nanostructured mechanisms.
Another technical field which has recently begun using three-dimensional or four-dimensional irradiation methods of this kind is in the medical technology sector. Here, too, it is typically necessary to deliver the highest possible dose to certain volume regions inside a body (such as a tumor), while the surrounding (healthy) tissue should either be subjected to the smallest possible dose or preferably not be subjected to essentially any dose at all. This is particularly true when the surrounding tissue constitutes so-called critical tissue such as sensitive organs (referred to in professional circles as an OAR, which stands for “organ at risk”). In this context, this can, for example, be the spinal cord, main blood vessels or neural nodes. Especially when irradiating moving target volumes, a large number of problems arise, some of which have not yet been solved or have not yet been solved to a satisfactory degree.
Essentially, there is a large number of possible solutions. Especially for use with scanning methods, for example, three special approaches will be discussed. These are so-called rescanning methods, gating methods and tracking methods.
In rescanning methods, the body to be irradiated is irradiated in a large number of irradiation scans. With a cyclically repeating movement pattern of the moving body (or of the target area to be irradiated), this therefore results in an irradiation of the target volume that is sufficiently powerful when averaged statistically.
In gating methods, an active irradiation of the target body takes place only when the volume region to be irradiated is in a relatively tightly restricted movement phase. At other times, however, no irradiation occurs.
Especially tracking methods are considered to show particular promise at this time. In tracking methods, the region on which the irradiation finally acts (for example, the zone of the Bragg peak) is moved in accordance with the movement of the volume region of the target body that is to be irradiated.
All three methods have in common the fact that the particle beam (more precisely, the main effective region of the particles) must move (scan) in all three spatial directions. In order to produce a scan in the z direction (the direction essentially parallel to the particle beam), it is thus necessary to vary the energy of the particles.
One possibility for implementing this lies in triggering the particle accelerator itself in a varying fashion so that it emits particles with different energies. The problem with this is that the variation of the particle energy in this case can only occur relatively slowly. In synchrotrons, for example, it has thus far been at best possible to vary the particle energy from one extraction cycle to the next. This results in energy adjustment times in the region of about 10 s. Particularly for tracking methods, adjustment times of this length are too long and are therefore unsuitable. But in rescanning methods and gating methods as well, such long adjustment times result in a significant amount of unnecessary loss in beam time.
The use of passive energy modulators has already been suggested as a possible solution. In these, the particle beam passes through an energy absorbing medium. Through a suitable adjusting mechanism, the medium can be changed in terms of its thickness (as “perceived” by the particle beam) so that the particle beam must travel a different distance through the energy absorbing material. This correspondingly changes the energy of the particles passing through. Examples of such absorber systems include wedge-like or double-wedge-like energy absorber systems. Fast-moving water columns and rotating modulator wheels have also been proposed. Here, too, there is ultimately a change in the distance that the particles must travel through the corresponding modulator material.
Even though such modulator systems are basically suitable for a rapid energy modulation, they still have disadvantages. For example, it has turned out that there can sometimes be considerable discrepancies between a “triggered” energy damping, (i.e. the input value of the control signal) and the actual energy damping by the modulator system. This results in corresponding inaccuracies in the processing method or treatment method, which is correspondingly disadvantageous.